Titanium-aluminum alloys



ATTORNEYS a By Roemer/.dAF-FEE.

Muwwfbgmmm W. L. FINLAY ET AL TITANIUM-ALUMINUM ALLOYS Filed April 23, 1954 March 1, 1955 ALUMINUM,PER CENT 2 United States Patent` O 2,103,278, TITANIUM-Awww A LnorsI WilteLfL. Finlay, Beaver, Pat, andJBruceiiW; `.(lonser, (Zdllimlius4 and.fillobertI L* Ja'fee, Worthington, 0h10, assignors, f vby directf and.v mesne assignments, 4toRem- .(lmr=Tillnim, Ic.; Midlandgl Pa., .a corporation 1 of Pennsylvania-i Application April 23, ,1954,-Seral=No0425,134-.

11 Claims. (Cl. 75175.5)

This invention pertains to binary allows of titanium and aluminum and also to ternary and highenalloyspf titanium and aluminum containing one or more of the interstitial elements carbon, oxygen and nitrogen.

This application is a continuation-in-part of. ou i:.co` pending application Serial No. 157,639, filed April 22, 1950; Serial No. 179,322, led August 14, 1950; and Serial No. 210,439, tiled February 10, 1951, now abandoned, which are in turn continuations-in-part of our. now abandoned applications Serial No. 66,:838, led, December 22, 1948, and Serial No. 95,152, led May 24,I 1949.

Substantially Pure titanium can be produced by the. socalle'd---iodide= :process described in Patent No. 1 ,6711,21'3 to 'VanArkeh butetheprocess isgslow -andiexpensiv Titanium iis 'accordingly:commercially produced-at -the present timeprncipally'bythemagnesinmreductionof titaniumftetrachloride;iii-'accordance with the process described infPatent- No.` 2,205-85 4 to Kroll, andamodifcations `thereof; Ducato-the presence:offcertain-^impurities; titanium of commercial-purity as .thus-produced; possesses fhigher strength and greater hardness than that obtained by the Van Arkel Ior iodide process.`

The present invention comprises in one of its aspectsthe discovery that strong and ductile ,binary alloys of titanium and aluminum are obtained over a critical'range of about 2.5 to 8% aluminum.

The :invention comprises in another ofits aspects the further; discovery that the strength of thefbinary'fal'loy is graftly` enhanced, without undue. loss of ductility2 by Controlled-additional1Qi-.one.,.0L- more of the interstitials carbon, oxygenandi-ni'trogon. Inrthe absence of appreciable amounts ofi oxygen and nitrogen-gimithe fallow the carbonimay range uputo about 0.6% on .the high side with aluminum up toiabout which additions as small as about ,0.051% are effective materially torstrengtlien the f 0,

binarygally. Thus .the addition o 0.05% `carbon enhancesfthetensilef strength by about 5,000i'p s. i. ,Atfhigher aluminum contents, the maximum carbonzmust be proportionately reduced down to: about 0.3% carbon atvfabout 7.5 aluminum.

In' the absence of appreciableamounts-gof carbon andnitrogen, oxygen may, range up to 0.35% on the high side with aluminum up to about-5%; with'out und-ue e m brittlementiof the alloy, the lower elective limit being about 10.05%, with the Samet enhancement in tensile strength asisabove indicated furthe lower carbon limit. The oxygen.; content 'should beton the lowside Afor Aaliirninum contents aupwards of 5%., i. e., above 5 %";aluimnum,-` totaljoxygen should notsexceed;about10.2%\

In the absence of :appreciable amounts-of carbon and j oxygen, thenitrogenncontent may rangeaup to 025% on z the highside for aluminum contents `.upyto` about? .5% without 2unduly embrittliig the aIIQy, the lower effective limit being. about' 0.1025 withthesame enhancement and strengthening effect as, the: lower limit additions .of carbon. and 'oxygen .above.noted, At ,upwardsfof..5%. .aluminum, totahnitrogen., shouldnot exceedabout 0;\15,%;

Inthe absenceof any appreciable content ofnitrogeii,

i. e., underabout 0.025%, .the. .cai bonmay,.range .upyto about 0.41%, Itogether with: oxygen upf to..about 02%, againwithaluminuni upftoabout 5%. Likewiseim-the allows containing both carbon and nitrogen,but.inap preciable amounts of oxygen, the carbon may range up to about 0.25% inncouiunction with nitrogen up to about ,0.2%. Where all'three elements, carbon, oxygen and nitiogel far-e pmsentgflhefcaltbon.ishouldz#not exceed about 0.25 and. the. total contento-f oxygen Y and nitrogen should not exceed .about 0.2%. The alloys containing over 0.4%. carbon are embr-tt-led byyadditionszo-'Dxygen or-nitrogen.

In the drawings, Fig-,l is` a se elongation and tensile iodide base titanium.- l to. 5 of aluminum.

Fig`. 2 is arcomposite` gnaph'showing theelongationand 0.2% olfset=yieldstrengthsl of numerousV iodide base titanium-aluminum -alloys containing -up--to l8%- ofaluminum.

It has been -found that 2%'l` of aluminum has aI ries of curves showing the properties of a series ofbinary aluminum ,alloys containingfrom the. addition `to'titanium of `1 to relatively vminor 1 effect, Athe properties of the resulting alloys not differingniateriall'ypfr'om th'ose of unalloyel titanium;

Assh'own in'Fig.l l, all'oysofl titanium with-1% num have, as vcomparedgwith unalloyedrtitanium, mate strength whichis but 'slightly' higher, and

11 ,strengthfA and a proportional limitl wli'ich-A are than those of the unalloyed metal. gat-ion is slight.

A very signicant change takes place in the region of an aluminum content of about 2.5%. The proportional limit and yield strength curves have actually reversed, both properties showing a defining increase. Ductility is diminished but is approaching a minimum value. As the aluminumcontent is further increased, say to 5%, the effect is even-more striking. The second 2.5% increment "produces :an improvement in tensile properties which is severaliimes that of the rst 2.5% increment, but without a proportionate loss of ductility that would be expected... Instead, the loss of ductility is almost negligible, andsubstantiallly less than that taking place between a zeroi aluminum content and a 2.5% aluminum content.

The; alloys of Fig. l were prepared and processed as follows;-

Ani-admixture of iodide titanium with the requisite amountjiof aluminum was melt cast under contaminationfreei conditions sby arc melting in a cold mold or Watercooled crucible in an inert or argon atmosphere. The resultingi'ingotf'was heated to a temperature of about 850 C., and-'rolled to a thickness of about 0.040, its thickness being reduced about 10% at each pass through the rolls, and:theingoti being reheated to about 850 C. after each p ass.` After-:being brought to the desired thickness, the strip was;mechanically cleaned and vacuum annealed for about.3 hours at a temperature of about 850 C. The properties graphically illustrated in Fig. 1, together with those of a 7 .5 aluminum alloy, are tabulated as follows:

Table I (IODLDE TITANIUM BASE) alumi- Vanultiayield nactually lower The change is elon- Fig. 2 shows graphically the relationship between 0.2% offset yield strength and elongation for alloys of titanium with up to about 8% aluminum, being a composite of the results of numerous tests. Attention is particularly invited to the rapid increase in strength with slight loss of ductility when the aluminum content exceeds about 2.5 These results are typical of many which the present applicants have secured for binary titanium-aluminum alloys subjected to a variety of processings, the titanium being either iodide or commercial purity titanium. For example, a series of alloys made with commercial purity titanium were subjected to the same processing as above outlined except that the final anneal at 850 C. was for a period of l5 minutes, instead of 3 hours, with the following results:

1050 C. between passes, in the as-rolled condition showed a Vickers hardness of 315; a proportional limit of 66,700; a 0.1% offset yield of 98,000, and a 0.2% offset yield of 103,500; an ultimate strength of 112,800; an elongation of l0; and an area reduction of 36.

These alloys are further characterized by their ability to maintain their hardness and strength at high temperatures. The hardness of an alloy of titanium with 5% aluminum materially exceeds that of 18-8 stainless steel at all temperatures up to 600 C., and is equal to the hardness of such steel at about 700 C., and only slightly lower at 800 C. The binary alloys of this invention are thus of exceptional value for high temperature service, where they are preferred to the stainless steels by reason of their lighter weight.

Again the improvement, if any, due to the use of up to 2% aluminum is slight, while at 5% very high strength with ample ductility is found.

For alloys of slightly higher aluminum content a higher rolling temperature, say l050 C., is preferred. For example, an alloy of iodide titanium with 8% aluminum, after rolling to a final thickness of 0.040" with a reduction of 10% per pass and a reheating to The following Table Ill shows the effect on mechanical properties of additions of one or more of carbon, oxygen and nitrogen to the titanium-aluminum alloys of the invention. The results are given for both iodide base and commercial purity base titanium alloys as indicated in the table. Also the properties are for the alloys in the annealed condition, the specimens having been prepared by rolling and annealing at 850 C.

Table IIL-Mechanical properties of Ti-Al and Ti-Al- (C, O, N) Alloys [Annealed condition] (IODIDE TITANIUM BASE) Composition, Percent Tensile Properties:

(Balance Titanium) pslX1,000 P t P t M ,u

ercen ercen Elongation Reduction grcs ,s v 0.2% Ultimate in l" in Area Lung Al C O 5 ,)f strength 2. 5 0. 25 66 75 24 55 272 5 0. 1 102 112 6 18 359 5 0. 2 122 131 22 43 404 5 0. 25 103 108 18 50 345 5 0. 4 116 121 18 47 365 5 0. 5 124 130 11 21 307 5 0. 6 122 123 18 27 415 5 0. 7 Brlttle Brittle Brittle Brittle Brittle 7 0. 25 124 125 18 39 390 7. 5 0. 1 111 20 40 358 7. 5 0. 2 119 17 46 372 7. 5 0. 25 117 25 48 377 7. 5 0. 3 129 21 45 390 7. 5 0. 4 135 22 306 7. 5 0. 5 131 7 28 408 10 0. 25 124 0 1 419 12. 5 0. 25 Brittle Brlttle Brlttle Brittle 5 0. 1 90 16 40 305 5 0. 2 97 13 29 346 7. 5 0. 1 Brittle Brittle Brlttle Brlttle 5 102 14 36 311 5 98 13 40 5 135 12 40 387 5 145 2 25 396 5 145 1 5 449 7. 5 106 38 354 10 Brlttle Brlttle Brittle Brittle 3 0. 25 0. 2 131 10 14 438 5 0. 25 0.025 130 15 25 439 5 0. 25 0. 05 132 13 18 444 5 0. 25 0. 1 116 19 49 397 5 0. 25 0. 2 130 19 45 400 5 0. 25 0. 3 93 0 0 475 5 0. 4 0. 2 140 140 1 2 412 5 0. 5 0. 2 Brittle Brlttle Buttle Brittle Brlttle 5 0. 25 0. 025 118 120 32 411 2. 3 5 0. 25 0. 05 112 14 23 409 2. 3 5 0. 25 O. 075 132 132 15 26 429 Brittle 5 0. 25 0. 1 115 122 35 367 5 0. 25 0. 2 135 135 9 450 Brlttle 7. 5 0. 25 0. 1 Brittla Brittle Brittle Brlttle Brittle Brittle -Ti-SAl l `binary yieldfand yultimate.

.[nnnealedeondition] noninaif'rlnltennunasan Composition, Peroent Tensile Properties:- (Balance *litaniunu4 z psiXtgDOo. l Mm 112mm *Percent Vickers 4nenti i Y 4 l u 'E19-www3 "Red-mon Hardness `Radius 0.2% Ultimate in 1" .in .Area f Y Lof A1 C o N onset g- :Yld Strongizh o; 25 0.2` 0. `925 1,41 '1 143 s 454 Buttle 5 0.`v 25 0.3 0.1025 91 0 0 481 .lBrittle 5 0.25 0. 2: -0.105; g .1,03 y0 0 476 Brittle 5 1 o. 25. 0.3 .o. .o5 102 o o 473 Brune. 5 0. j 0. 2' 0. 075 137 0 0 458 Brittle 5 r0. `0.1 `0.1' r133 .1 a9 443 5 I Oi l0. 2g v 01.1 82 0 0 477 Brittle 5 0. 0.1 116 12 25 337 {GONEVEHGIAL' BUBITY TlTNUMsBASEl 4 0. 1 1.99. .105 I 17f- :49 324 1. 7 4 0; 2 1.108.- 113 ..19 n.52 345 1. 8 5 o. 1 12s :1,33 1:5 l:11 402 5. o 5 0. 2 122 rH11 .22 404 2. 4 5 0.25 ..137 -143 18 137 427 5. 5 z. 4 .10.25 w10? l115 17.v 46 355 2. 6 4 10. 35v 119. .127 13 Y 29 380 2. 7 5 ,10. 25 199 118` f. .17- V37 405 3. 1 5 "10.135 .'123 i132 1 9 33 411 3.5 4 -01 1 110 117. 17 :42 350 1. 8 5v 0.1 130 H137 14 T38 398 2. 5 0. 1 0. 1 l 106 2116 12 .25 337 1, Includes4 0.15% oxygen-present nnunalloyed titanium-.basemetal; tents were 4suticiently small to benegleoted From .the .above data tit. willbe, seen ,that..;tl1e binary of .up to. .abouti-l0.6.%. Thus, .Whereas.theA iodidev .:base rengths." And. tensile elongation valuesare, respeofis1e-ly'153,v p s. i. and 17,5%.,ffin 'the'. '1`i-.5A150,6;C V ternarLtheSe values'becorne.A 122,10'00.p..s.1i., 123.501)() p... slr-i. andi.18%. Thus the yieldv strength;` has.. been.: doubled, and; 'the' tensile strength increased :by/5.0%v with no1 .loss of duQtility.-

A tupwar'ds, of 5 aluminum Ithe. carbon contentvr liould be correspondingly reducedfif adeqnateiductil "1s tobe retained. Thus the 'fiodid. base'."Ti,.'/l`.5.^il"y 1Y`has an ultimate strength .(")f'9.7..,-0.00r p.. s.; i. .and a, tensile. l

.vgation of 122%, as. compared. .toan ultimate. of"1`2 000 p. s. i. and an elongation of'181%forthe'Ti75A 25C the-'nitrogen and carbon con- =i0;2%. falthough with considerable-,f

ternary alloy- V`Her.e-asain Inarltsai.strengthening'With*110V noticeable loss. ofduot1ity `results from .the carbon addition.

T he ultimate Strength. of. alloys .of.tli,ta .niur n withgabout 7.5% aluminum.; iszinereasedl by. additionstof carbon up .to aboutv 0.3%. '.I'hesealloys-hayeLthepecliarityiof `sustaininga maximum. load withanelongation less than 0.1%,1 then -elongating.,about..2 0%., withan.area. reduc- Y tion .inzexcess `of 40% .before failure. `.They-.are ,rendered brittle by` the presence of-more 'thanahout' 0.3%. carbon,

- the `0.3 figure substantially .coincidingfwith the solubility 'ofY carbon in alpha titanium. '.'Thealloy's containingf`57% aluminum Y with about 50.31% cai-bon, will not tolerate .more than .a few..hundr e dths .of one percentof .either oxygen or. nitro geri,l.ae1'nie.tonnel'etal-y-l elnhrittled bYIOJ- 1% of either.

As further shown by the Table III`data`, for aluminum contents npvto about 5%.` the total oxygen eontentin lin the absence of appreoiableu amounts Vtif-.carbon and nitrogen may range un to a. total offabout 111.35% Het@ asain, marked. strengthening is; obtained 'with nonieterial eiect on ducti'lity omparingzthe `valueksffor the vComlneroial.- purity titaniunn base alloys," the. 'Ti-SAI binary has an ultimate of"121,`000.p s: ifand'an loggation of 1.6%, as against an ultimatel (551312,00 .ys 1 and an elongation of v1,9% for -the .T1-5 -0 35,0

'should'.beheld' on 'the 'low 'sitleandrnot 11o exceed? total ofxbout-O-Za/- ternary. Above.5% .aluminuni,..the total' oxygen-content and: :elongations 1 are t'.

The data' furtherl showsthatrthese 'ialloys' con up'=to':5% .aluminumuand up'.` to" .4%vearbon,k therstrengthenedby additionsfoffeoxygenfupit a loss of du'c'tihty-,jthe ultimate u without i and with Y ithe 1 .oxygen addition Hbeing :121,000 c and 140,000, respectivelygivith corresponding Y Upftto thel0`.25%l carbon level, however, 1considerable@strengthening 4-ocourswvith no' loss lof ductilityy the..comparisonsln fo'rlfthe" =i1ltimtes 1.08,'000've13sus 130;000 and-518% versus 19%, respectively, for tithe dfi-SAI` vfand fTi-5Al-0.25C10.2,Oalloys. 1nthe@alloys"fofthissgroup, the nitrogen contentgshould note. exceed 0.025%, as further shown by the Table-111 data. .,"Ihatdataalso shows .that with carbon in excess of .0.4%,..t1heseea1loys-are embrittled by .the presence .of appreciable amounts of oxygen and/or nitrogen.

Inthe.4 absence. of .signiicantnngountsf .oioxygn y the alloys oontainingnp to.5% aluminum and.:np1ft'o`0.25% `carbon, arebenefitedbyV additions :of nitrogen up to about-01.1% nitrogen, but .become VquiteJAuitt-Ie `forahiglier nitrogen additions. At thel 0.1% fnitrogen level .the lstrength kand ductility comparisons withoutfandy'lithlthis addition are 108,000versus 122,000 p.; s; i. for the tensiles tand 18% versus 15% for the` corresponding elongations. With this group of alloys the total. oxygen. and nitrogen should not exceed. about 0.2%.

The alloys of the invention having tensile elongations as low as 1 aor 2% are useful forgings and those radius as high'as"20"1 are 115eful in s heet form. c The alloys of the inventions-have excellent"-co1d^work- .mg-properties 'asshown Vby ethemdatajfonf-edg .racking limits versus percent reduction given in the following Table IV: Table IV.-Cold working properties for Ti-Al and Ti-Al plus C, O, N alloys (COMMERCIAL PURITY TITANIUM BASE) Qold Roll- VHN at Compositionl percent (Balance VHN (Anlfae du"0Ie' Titanium) iiealed) Limity pegr C 01d Rolf cent red. ing

1 Dld not crnck at maximum reduction shown, I Hardness at maximum reduction in edge-cracking test.

Referring to the above data, it will be seen that the' iodide titanium-base alloys containing up to 5% aluminum were cold reduced up to at least before edge cracking occurred, and even at substantially the upper limit ofl 7.5% aluminum, reductions up to about 30% were obtained. For the commercial purity titanium-base binary alloys, the percent cold reduction up to the edge cracking limit was slightly lower for a given aluminum addition than for the iodide titanium-base alloys, al-

-though the reductions are roughly comparable Within about 5% or so. Excellent cold reduction properties are also shown for the ternary and higher order alloys con taining one or more of carbon, oxygen and nitrogen.

The effect of the vcold working in increasing the hardness is shown by the Vickers hardness values (VHN) of each alloy in the annealed condition as compared to that after cold working. The work hardening response of these alloys is further illustrated by the yield strength values given in the following Table V:

Table V.-Yeld strengthens of cold-worked Ti-Al and Ti-Al plus C, O, N alloys (COMMERCIAL PURITY TITANIUM BASE) V l Predicted from flow curves obtained dun'ng tensile tests of annealed material.

It will be seen that cold working markedly increases the strength of these alloys.

What is claimed is:

l. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum, up to 0.6% carbon, up to 0.35% oxygen and up to 0.25 nitrogen, said elements being present in such relative proportions, and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength at least 30% in excess of that of the unalloyed titanium base metal.

2. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum, up to 0.6% carbon, up to 0.35% oxygen and up to 0.25% nitrogen, as produced by melting the alloying elements in such relative proportions and under conditions suflciently free from other elements tending to reduce ductility, as to provide a resulting alloy having a minimum tensile elongation of about 10% and an ultimate strength at least 30% in excess of that of the unalloyed titanium base metal.

3. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum and at least one element selected from the group consisting of 0.05 to 0.6% carbon, 0.05 to 0.35% oxygen and 0.025 to 0.25 nitrogen, said elements being present in such relative proportions, and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. i.

4. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum and at least one element selected from the group consisting of carbon, oxygen and nitrogen in minimuiri amount of 0.1% and in maximum amount of 0.6% for carbon, 0.3% for oxygen and 0.25 for nitrogen, said elements being present in such relative proportions and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. i.

5. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum, 0.05 to 0.4% carbon and 0.05 to 0.2% oxygen, said elements being present in such relative proportions and said alloy being suiiiciently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. i.

6. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum, 0.05 to 0.25% carbon and 0.025 to 0.2% nitrogen, said elements being present in such relative proportions and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. 1.

7. A titanium base alloy consisting essentially of about: 2.5 to 8% aluminum, 0.05 to 0.25% carbon, 0.025 to 0.2% of at least one element of the group oxygen and nitrogen, said elements being present in such relative proportions and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. i.

8. An alloy consisting of about: 2.5 to 8% aluminum, up to 0.6% carbon, up to 0.35% oxygen, up to 0.25% nitrogen, and the balance titanium, said elements being present in such relative proportions, and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength at least 30%lin excess of that of the unalloyed titanium base meta 9. Ari alloy consisting of about: 2.5 to 8% aluminum, up to 0.6% carbon, up to 0.35% oxygen, up to 0.25% nitrogen, and the balance titanium, as produced by melting the alloying elements in such relative proportions and under conditions sufliciently free from other elements tending to reduce ductility, as to provide a resulting alloy having a minimum tensile elongation of about 10% and an ultimate strength at least 30% in excess of that of the unalloyed titanium base metal.

10. An alloy consisting of about: 2.5 to 8% aluminum, at least one element selected from the group consisting of 0.05 to 0.6% carbon, 0.05 to 0.35 oxygen and 0.025 to 0.25 nitrogen, balance titanium, said elements being present in such relative proportions and said alloy being sufficiently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength of at least 100,000 p. s. i.

11. An alloy consisting of about: 2.5 to 8% aluminum, at least one element selected from the group consisting of carbon, oxygen and nitrogen, in minimum amount of 1% and in maximum amount of 0.6% for carbon, 0.35% for oxygen and 0.25% for nitrogen, balance titanium, said elements being present in such relative proportions and said alloy being suciently free from other alloying elements tending to reduce ductility as to impart to said alloy a minimum tensile elongation of about 10% and an ultimate strength at least 30% in excess of that of the unalloyed titanium base metal.

References Cited in the le of this patent UNITED STATES PATENTS 1,648,954 Marden Nov. 15, 1927 2,370,289 Chandler Feb. 17, 1945 2,464,836 Thomas g Mar. 22, 1949 l() FOREIGN PATENTS Germany Mar. 24, 1942 OTHER REFERENCES Zeitschrift fr Anorganische Chemie; Begrndet von Gerhard Kruss (1910), Band 65, pp. 388 thru 393.

Mellor Comprehensive Treatise. on Inorganic and Theoretical Chemistry, vol. 7, page 10, published 1927.

Zeitschrift fr Metallkunde, vol. 29 (1937), Kroll,

pages 189-192.

ganic Chemistry, 1944 International Correspondence Schools Textbook Inorpart II, page 2.6, first ed., Copyright 

1. A TITANIUM BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT: 2.5 TO 8% ALUMINUM, UP TO 0.6% CARBON, UP TO 0.35% OXYGEN AND UP TO 0.25% NITROGEN, SAID ELEMENTS BEING PRESENT IN SUCH RELATIVE PROPORTIONS, AND SAID ALLOY BEING SUFFICIENTLY FREE FROM OTHER ALLOYING ELEMENTS TENDING TO REDUCE DUCTILITY AS TO IMPACT TO SAID ALLOY A MINIMUM TENSILE ELONGATION OF ABOUT 10% AND AN ULTIMATE STRENGHT AT LEAST 30% IN EXCESS OF THAT THE UNALLOYED TITANIUM BASE METAL. 